Microbolometer focal plane array systems and methods

ABSTRACT

Systems and methods for microbolometer focal plane arrays are disclosed. For example, in accordance with an embodiment of the present invention, microbolometer focal plane array circuitry is disclosed for a microbolometer array having shared contacts between adjacent microbolometers. Various techniques may be applied to compensate for non-uniformities, such as for example, to allow operation over a calibrated temperature range.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part application of U.S. applicationSer. No. 10/085,226, filed Feb. 27, 2002, which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

[0002] The present invention relates generally to focal plane arraysand, more particularly, to microbolometer focal plane arrays.

BACKGROUND

[0003] Microbolometer structures are generally fabricated on monolithicsilicon substrates to form an array of microbolometers, with eachmicrobolometer functioning as a pixel to produce a two-dimensionalimage. The change in resistance of each microbolometer is translatedinto a time-multiplexed electrical signal by circuitry known as the readout integrated circuit (ROIC). The combination of the ROIC and themicrobolometer array are commonly known as a microbolometer focal planearray (FPA). Additional details regarding microbolometers may be found,for example, in U.S. Pat. Nos. 5,756,999 and 6,028,309, which are hereinincorporated by reference in their entirety.

[0004] Each microbolometer in the array is generally formed with twoseparate contacts, which are not shared with adjacent microbolometers inthe array. One contact is used to provide a reference voltage for themicrobolometer while the other contact provides a signal path from themicrobolometer to the ROIC. A drawback of having two contacts permicrobolometer is that the contacts do not scale proportionally assemiconductor processing technologies transition to smaller dimensions.Consequently, as microbolometer dimensions are reduced, the contactsconsume a greater percentage of the area designated for themicrobolometer, which reduces the area available for the desiredresistive portion of the microbolometer and impacts microbolometerperformance. As a result, there is a need for improved techniques forimplementing microbolometer focal plane arrays.

SUMMARY

[0005] Systems and methods are disclosed herein to providemicrobolometer focal plane arrays. For example, in accordance with anembodiment of the present invention, microbolometer focal plane arraycircuitry is disclosed for a microbolometer array having shared contactsbetween adjacent microbolometers. Each microbolometer may be selected bya method that may reduce the amount of crosstalk and capacitivedegradations that may be associated with the shared contacts.Furthermore, the focal plane array circuitry may compensate fornon-uniformities (e.g., a temperature coefficient of resistance) toallow operation over a wider temperature range than with conventionaldevices. Additionally, techniques are disclosed to calibrate the arrayand/or circuitry, such as for example over a desired temperature range.

[0006] More specifically, in accordance with one embodiment of thepresent invention, a circuit includes a plurality of microbolometersforming a microbolometer array, wherein contacts within themicrobolometer array are shared among the microbolometers; means forselecting from among the microbolometers in the microbolometer array andproviding a corresponding output signal; and means for providingtemperature compensation for the output signal.

[0007] In accordance with another embodiment of the present invention, amethod of providing calibrated output signals from a microbolometerfocal plane array having shared contacts includes selecting at least onerow of the microbolometer focal plane array to provide correspondingoutput signals from microbolometers in the row; providing a trimresistor value to provide temperature compensation for at least onemicrobolometer in the row; and providing an offset value to providetemperature compensation for at least one microbolometer in the row.

[0008] In accordance with another embodiment of the present invention, amicrobolometer focal plane array includes a plurality of microbolometersforming a microbolometer array, wherein contacts within themicrobolometer array are shared by the microbolometers; a firstplurality of switches adapted to provide a reference signal torespective ones of the plurality of microbolometers; and a secondplurality of switches adapted to receive an output signal fromrespective ones of the plurality of microbolometers, wherein the firstand second plurality of switches are initially asserted and deasserted,respectively, with one of the switches from the first pluralitydeasserted prior to one of the switches from the second plurality beingasserted which couple to the same contact, with this switching patternrepeated for the first and second plurality of switches until the secondplurality of switches are all asserted.

[0009] The scope of the invention is defined by the claims, which areincorporated into this section by reference. A more completeunderstanding of embodiments of the present invention will be affordedto those skilled in the art, as well as a realization of additionaladvantages thereof, by a consideration of the following detaileddescription of one or more embodiments. Reference will be made to theappended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1a shows a circuit diagram illustrating a microbolometerarray and selection circuitry in accordance with an embodiment of thepresent invention.

[0011]FIG. 1b shows a circuit diagram illustrating a microbolometerarray and selection circuitry in accordance with an embodiment of thepresent invention.

[0012]FIG. 1c shows a circuit diagram illustrating a microbolometerarray and selection circuitry in accordance with an embodiment of thepresent invention.

[0013]FIG. 2a shows a timing diagram for the selection circuitry of FIG.1a.

[0014]FIG. 2b shows a timing diagram for the selection circuitry of FIG.1b.

[0015]FIG. 2c shows a timing diagram for the selection circuitry of FIG.1c.

[0016]FIG. 3 shows a physical layout of a microbolometer array inaccordance with an embodiment of the present invention.

[0017]FIG. 4 shows a physical layout of a microbolometer array inaccordance with an embodiment of the present invention.

[0018]FIG. 5 shows a physical layout of a microbolometer array inaccordance with an embodiment of the present invention.

[0019]FIG. 6 shows a physical layout of a microbolometer array inaccordance with an embodiment of the present invention.

[0020]FIG. 7 shows a physical layout of a microbolometer array inaccordance with an embodiment of the present invention.

[0021]FIG. 8 shows a block diagram illustrating a microbolometer focalplane array and associated circuitry in accordance with an embodiment ofthe present invention.

[0022]FIG. 9 shows a block diagram illustrating a microbolometer focalplane array and associated circuitry in accordance with an embodiment ofthe present invention.

[0023]FIG. 10a shows a circuit diagram illustrating a portion of areadout integrated circuit in accordance with an embodiment of thepresent invention.

[0024]FIG. 10b shows a circuit diagram illustrating a portion of areadout integrated circuit in accordance with an embodiment of thepresent invention.

[0025]FIG. 10c shows a circuit diagram illustrating a portion of areadout integrated circuit in accordance with an embodiment of thepresent invention.

[0026]FIG. 11 shows a circuit diagram illustrating a portion of areadout integrated circuit in accordance with an embodiment of thepresent invention.

[0027]FIG. 12 shows a flowchart of a calibration process in accordancewith an embodiment of the present invention.

[0028]FIG. 13 shows a detailed flowchart for a step of the flowchart ofFIG. 12.

[0029]FIG. 14 shows a detailed flowchart for a step of the flowchart ofFIG. 12.

[0030]FIG. 15 shows a detailed flowchart for a step of the flowchart ofFIG. 12.

[0031]FIG. 16 shows a detailed flowchart for a step of the flowchart ofFIG. 12.

[0032]FIG. 17 shows a compensation process in accordance with anembodiment of the present invention.

[0033] Embodiments of the present invention and their advantages arebest understood by referring to the detailed description that follows.It should be appreciated that like reference numerals are used toidentify like elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

[0034]FIG. 1a shows a circuit 300 illustrating a microbolometer arrayand selection circuitry in accordance with an embodiment of the presentinvention. Circuit 300 includes microbolometers 302 and switches 304.Microbolometers 302 (which are separately referenced as microbolometers302(1) through 302(N), where N represents the desired number ofmicrobolometers in a column) form at least a portion of an exemplarymicrobolometer array of at least one column of N rows, with adjacent(e.g., column neighbors within a column) microbolometers 302 sharing acontact 306. The number of columns and rows of the microbolometer arraymay vary, depending for example on the desired application, with circuit300 replicated to form the desired number of additional columns. Itshould also be understood that reference to a column or a row mayinclude a partial column or a partial row and that the column and rowterminology may be interchangeable, depending upon the application.

[0035] Switches 304 are employed to select the desired row within themicrobolometer array. For example, FIG. 2a shows an exemplary timingdiagram 320 for the selection circuitry of FIG. 1a (circuit 300).Control signals (labeled SEL1 through SELN) are used to controlcorresponding switches 304 (e.g., transistors within the ROIC) to selectthe desired microbolometer row. For example, if the control signal SEL1is asserted, switches 304(1) are closed and microbolometer 302(1)receives a reference voltage (labeled VDETCOM and also referred to asVbias, with its value set to, for example, ground or a desired voltagevalue) and provides a signal to associated or additional circuitry ofthe ROIC. In a similar fashion, microbolometers 302(2) through 302(N)may be selected, for example, row by row in a sequential fashion asshown in FIG. 2a.

[0036] As shown in FIG. 1a, microbolometers 302 within circuit 300 sharea contact (contact 306) with an adjacent microbolometer 302 within thecolumn. By sharing contacts, the number of contacts required for themicrobolometer array is reduced and, consequently, the amount of arearequired for the contacts is reduced. However, this may affect theperformance of the microbolometer array and hamper the ROIC's ability tocapture data from the microbolometer array. For example, additionalparasitic capacitances, capacitive loading, and switch resistance maysignificantly degrade the array's performance. Furthermore, additionalfactors or non-uniformities may contribute to the performancedegradation, especially if temperature variations occur, such as forexample temperature coefficient of resistance (TCR), heat capacity,thermal conductivity of each microbolometer 302, and self heating.Techniques for minimizing one or more of these performance degradationsare described in further detail herein.

[0037]FIG. 1b shows a circuit 330 illustrating a microbolometer arrayand selection circuitry in accordance with an embodiment of the presentinvention. Circuit 330 is similar to circuit 300 (FIG. 1a), but switches304 are controlled in a different manner. For example, FIG. 2b shows anexemplary timing diagram 340 for the selection circuitry of FIG. 1b(circuit 340). Control signals (labeled ENS through ENN and SELL throughSELN) are used to control corresponding switches 304 to select thedesired microbolometer row.

[0038] For example, initially the control signals EN1 through ENN areasserted to close associated switches 304(1) through 304(N) and applythe reference voltage (VDETCOM) to microbolometers 302(1) through302(N). The control signal SELL is asserted to close associated switch304(1), with microbolometer 302(1) providing a signal to associated oradditional circuitry of the ROIC. The control signal EN1 is deassertedto open switch 304(1) and remove the reference voltage frommicrobolometer 302(1). The control signal SEL2 is then asserted to closeassociated switch 304(2), with microbolometer 302(2) providing a signalto associated or additional circuitry of the ROIC.

[0039] In a similar fashion, microbolometers 302(3) through 302(N) maybe selected, for example, row by row in a sequential fashion as shown inFIG. 2b. After sampling microbolometers 302(1) through microbolometers302(N), the control signals SELL through SELN are deasserted and timingdiagram 340 may be repeated. By closing the select switches (e.g.,switches 304) in this manner, the detrimental parasitic resistance andcapacitance characteristics may be minimized, thus providing improvedperformance. Therefore, by controlling switches 304 as illustrated inFIG. 2b, capacitive loading and parasitic capacitances may be reducedand the microbolometer array's performance improved.

[0040]FIG. 1c shows a circuit 350 illustrating a microbolometer arrayand selection circuitry in accordance with an embodiment of the presentinvention. Circuit 350 includes microbolometers 302 and switches 304.Microbolometers 302(1) through 302(6) form one column of microbolometers302, while microbolometers 302(7) through 302(12) form another column ofmicrobolometers 302 in the microbolometer array. It should beunderstood, however, that circuit 350 may include any number ofmicrobolometers 302 to form the desired number of rows and that circuit350 may be replicated to form the desired number of additional columnsfor the microbolometer array.

[0041] Microbolometers 302 within circuit 350 share contacts within acolumn, such as for example contacts 352 for a first column and contacts354 for a second column. Microbolometers 302 within circuit 350 alsoshare contacts between the first and second column, such as for examplecontacts 356, with microbolometers 302(2), 302(3), 302(8), and 302(9)sharing contact 356(1) and microbolometers 302(4), 302(5), 302(10), and302(11) sharing contact 356(2).

[0042] Switches 304 are employed to select the desired row within themicrobolometer array. For example, FIG. 2c shows an exemplary timingdiagram 370 for the selection circuitry of FIG. 1c (circuit 350).Control signals (labeled SEL1,2; EN1; EN2,3; SEL3,4; EN4,5; and SEL5,6)are used to control corresponding switches 304 to select the desiredmicrobolometer row.

[0043] For example, the control signal SEL1,2 is asserted to closeassociated switches 304(5) and 304(10) and the control signal EN1 isasserted to close associated switch 304(4) and apply the referencevoltage (VDETCOM) so that microbolometers 302(6) and 302(12) can providetheir signals to associated or additional circuitry of the ROIC. Thecontrol signal EN1 is then deasserted to open switch 304(4), the controlsignal EN2,3 is then asserted to close associated switch 304(3) andapply the reference voltage (VDETCOM) so that microbolometers 302(5) and302(11) can provide their signals to associated or additional circuitryof the ROIC.

[0044] The control signal SEL1,2 is then deasserted to open switches304(5) and 304(10) followed by the control signal SEL3,4 asserted toclose associated switches 304(6) and 304(9) so that microbolometers302(4) and 302(10) can provide their signals to associated or additionalcircuitry of the ROIC. Thus, this process may continue in a similarfashion to read out the signals from microbolometers 302(1) through302(3) and 302(7) through 302(9), for example, row by row in asequential fashion as shown in FIG. 2c for the associated controlsignals of circuit 350.

[0045]FIG. 3 shows a physical layout of a microbolometer array 500 inaccordance with an embodiment of the present invention. Microbolometerarray 500 includes microbolometers 502 and 504, which are arranged asone column of two rows and may represent two of microbolometers 302(e.g., microbolometers 302(1) and 302(2) in FIGS. 1a or 1 b) withincircuit 300 or 330.

[0046] Microbolometers 502 and 504 each include a resistive material506, which is formed of a high temperature coefficient of resistivity(TCR) material (e.g., vanadium oxide (VO_(x)) or amorphous silicon).Resistive material 506 is suspended on a bridge 508, with resistivematerial 506 coupled to its contacts 514 via legs 512. Legs 512 attachto resistive material 506 through a resistive material contact 510(e.g., a leg metal to resistive metal contact and labeled VO_(x)contact). In general, microbolometers 502 and 504 are constructed in aconventional manner with conventional materials, but share contact514(3).

[0047]FIG. 4 shows a physical layout of a microbolometer array 540 inaccordance with an embodiment of the present invention. Microbolometerarray 540 is similar to microbolometer array 500 (FIG. 3), but contacts514 are oriented in a different manner, as shown, relative tomicrobolometers 502 and 504. Microbolometer array 540 may allow astronger bond between leg 512 and contact 514 and/or may be easier toform during the manufacturing process.

[0048] Microbolometer array 500 (FIG. 3) or microbolometer array 540(FIG. 4) may be implemented as an array of any desired size (e.g., 644by 512 pixels with each pixel (or microbolometer) 25 by 25 μm in size).For example, FIG. 5 shows a physical layout of a microbolometer array550 in accordance with an embodiment of the present invention.Microbolometer array 550 is a four-by-four array having microbolometersimplemented as described in reference to FIG. 3.

[0049]FIG. 6 shows a physical layout of a microbolometer array 600 inaccordance with an embodiment of the present invention. Microbolometerarray 600 includes microbolometers 602, 604, 606, and 608, which arearranged as two columns of two rows (e.g., microbolometers 602 and 604forming one column and microbolometers 606 and 608 forming the othercolumn).

[0050] In general, microbolometers 602 through 608 are constructed in amanner similar to, for example, microbolometer 502 (FIG. 3). However,microbolometers 602 through 608 are arranged to all share contact514(3), shown centrally within FIG. 6. Thus, microbolometers 602 through608 may represent, for example, four of microbolometers 302 (e.g.,microbolometers 302(4), 302(5), 302(10), and 302(11) in FIG. 1c) ofcircuit 350. Furthermore, microbolometer array 600 may be replicated toimplement an array of any desired size. For example, FIG. 7 shows aphysical layout of a microbolometer array 650 in accordance with anembodiment of the present invention. Microbolometer array 650 is afour-by-four array having microbolometers implemented as described inreference to FIG. 6.

[0051]FIG. 8 shows a block diagram 800 illustrating a microbolometerfocal plane array 802, with uniformity-correction circuitry, andinterface system electronics 818 in accordance with an embodiment of thepresent invention. Microbolometer focal plane array 802 includes amicrobolometer array (labeled unit cell array) and a readout integratedcircuit (ROIC) having control circuitry, timing circuitry, biascircuitry, row and column addressing circuitry, column amplifiers, andassociated electronics to provide output signals that are digitized byan analog-to-digital (A/D) converter 804.

[0052] The microbolometer array (unit cell array) of microbolometerfocal plane array 802 may be formed by microbolometers having sharedcontacts and selection switches as described in reference to FIGS. 1-7.The ROIC of microbolometer focal plane array 802 may be employed tocontrol the selection switches (i.e., switches 304 of FIGS. 1a, 1 b, or1 c which may be formed as part of the ROIC) to select the desiredmicrobolometers for obtaining the desired output signals. The columnamplifiers and other circuitry of the ROIC may otherwise be constructedin a conventional manner.

[0053] The A/D converter 804 may be located on or off the ROIC. Theoutput signals from A/D converter 804 are stored in a frame memory 806.The data in frame memory 806 is then available to image displayelectronics 808 and a data processor 812, which also has a dataprocessor memory 810. A timing generator 814 provides system timing.

[0054] Data processor 812 generates uniformity-correction data words,which are loaded into a data register load circuitry 816 that providesthe interface to load the correction data into the ROIC. In this fashionthe digital-to-analog converters, and other variable circuitry, whichcontrol voltage levels, biasing, circuit element values, etc., arecontrolled by data processor 812 to provide the desired output signalsfrom microbolometer focal plane array 802.

[0055]FIG. 9 shows a block diagram 280 illustrating a microbolometerfocal plane array 282, with uniformity-correction circuitry, andinterface system electronics 283 in accordance with an embodiment of thepresent invention. Block diagram 280 is similar to block diagram 800,but includes additional techniques for providing, for example,temperature compensation and/or correction for various non-uniformities,as described in further detail herein (e.g., in reference to FIGS.10-17).

[0056] Microbolometer focal plane array 282 includes a microbolometerfocal plane array (labeled unit cell array) and a readout integratedcircuit (ROIC) having control circuitry, timing circuitry, biascircuitry, row and column addressing circuitry, column amplifiers, andassociated electronics to provide output signals that are digitized byan analog-to-digital (A/D) converter 284.

[0057] The microbolometer array (unit cell array) of microbolometerfocal plane array 282 may be formed by microbolometers having sharedcontacts and selection switches as described in reference to FIGS. 1-7.The ROIC of microbolometer focal plane array 282 may be employed tocontrol the selection switches (i.e., switches 304 of FIGS. 1a, 1 b, or1 c which may be formed as part of the ROIC) to select the desiredmicrobolometers for obtaining the desired output signals.

[0058] The A/D converter 284 may be located on or off the ROIC. Theoutput signals from A/D converter 284 are adjusted by a non-uniformitycorrection circuit (NUC) 285, which applies temperature dependentcompensation (e.g., Lagrange Offset, Temperature Dependent Gain, andadditional Offset) as discussed herein, such as for example in referenceto FIGS. 12-17. After processing by NUC 285, the output signals arestored in a frame memory 286. The data in frame memory 286 is thenavailable to image display electronics 288 and a data processor 292,which also has a data processor memory 290. A timing generator 294provides system timing.

[0059] Data processor 292 generates uniformity-correction data words,which are loaded into a correction coefficient memory 298. A dataregister load circuitry 296 provides the interface to load thecorrection data into readout integrated circuit 282. In this fashion thevariable resistors, digital-to-analog converters, and other variablecircuitry, which control voltage levels, biasing, circuit elementvalues, etc., may be controlled by data processor 292 so that the outputsignals from the readout integrated circuit are uniform over a widetemperature range.

[0060]FIG. 10a shows a circuit 1000 illustrating a portion of a readoutintegrated circuit 1002 and circuit 330 (e.g., a portion of amicrobolometer array, such as a row or a column) in accordance with anembodiment of the present invention. Circuit 1002 provides temperaturecompensation for circuit 330 in accordance with an embodiment of thepresent invention. It should be understood that circuit 330 is shown inan exemplary fashion and that circuit 300 (FIG. 1a) or circuit 350 (FIG.1c) may be substituted for circuit 330 (e.g., in FIGS. 10a, 10 b, or11).

[0061] Circuit 1002 includes supply voltage 40 (and may provide thereference voltage labeled VDETCOM), thermally-shorted microbolometer 36,resistors 26 and 38, transistor 30, amplifier 32, and adigital-to-analog converter (DAC) 34. As explained in detail herein,circuit 1002 provides substrate temperature compensation and temperaturecoefficient of resistance (TCR) mismatch compensation for the active andload microbolometers.

[0062] The active microbolometer is the thermally isolatedmicrobolometer, selected from circuit 330 as explained above, whichreceives incident infrared radiation. The active microbolometer isbiased by the reference voltage (VDETCOM) and a load current (Ibias).Amplifier 32 provides the gate bias for transistor 30 (an NMOStransistor), while DAC 34 is used to set an amplifier reference voltageand control amplifier 32 to set the appropriate gate bias for transistor30. Alternatively, amplifier 32 can be eliminated and DAC 34 used to setthe appropriate gate bias directly for transistor 30. A load circuit orbias circuit includes supply voltage 40, resistor 38, microbolometer 36(thermally shorted (to the substrate) load microbolometer), transistor30, and amplifier 32 with DAC 34, which are used to establish the loadcurrent (Ibias).

[0063] Microbolometer 36 is used as a substrate temperature compensatedload. Supply voltage 40 is set to optimize the operating point forcircuit 1002 by setting the nominal voltage drop across microbolometer36. An output voltage (Vout) 42 of circuit 1002 is provided at a node41.

[0064] An amplifier (such as an amplifier 28 as illustrated in FIG. 11)may amplify a voltage at node 41 to provide an output voltage (Vout) 42.The amplifier is an exemplary circuit element to provide amplificationor buffering for the voltage at node 41, if desired. As with amplifier32, a DAC may provide a reference voltage (Vref) for the amplifier orthe reference voltage may be at a set voltage level (e.g., ground). Itshould be apparent that output voltage (Vout) 42 may be translated,amplified, or converted by amplification or integration processes and/orother well known signal processing techniques.

[0065] For example, a transimpedance amplifier 258 (as illustrated incircuit 1050 of FIG. 10b) may be employed within a portion of a readoutintegrated circuit 1052 to provide the output voltage 42. In addition, aDAC 256 may control the gate terminal of transistor 30, while a DAC 254controls a gate terminal of a transistor 252 coupled to resistor 26.Thus, transistor 252 along with transistor 30 may control the biasapplied to the active microbolometer (selected from circuit 330) andmicrobolometer 36, respectively. Specifically, DAC 254 adjusts theoffset by controlling the bias applied to the active microbolometer incombination with resistor 26 via transistor 252. Likewise, DAC 256adjusts the offset by controlling the bias applied to microbolometer 36in series with resistor 38 via transistor 30.

[0066] Transimpedance amplifier 258, having an impedance element 260(e.g., a capacitor, a switched capacitor network, or a thermally-shortedmicrobolometer that may compensate gain as a function of substratetemperature), translates the current level flowing into transimpedanceamplifier 258 into a voltage level at output voltage (Vout) 42.Consequently, DACs 254 and 256 determine the amount of current flowingthrough respective microbolometers (i.e., the active microbolometer andmicrobolometer 36) and also into transimpedance amplifier 258 and, thus,set the offset and reference level of output voltage (Vout) 42. DACs 254and 256 can be calibrated, as discussed herein, for a single temperatureor over a desired operating temperature range for each microbolometer inthe FPA array.

[0067] In terms of general circuit operation for circuit 1000 (FIG.10a), as incident infrared radiation levels increase, the temperature ofthe active microbolometer (i.e., one of microbolometers 302(1) through302(N)) increases, which lowers its resistance and reduces the voltagedrop across it and thus, increases the voltage level at the drainterminal of transistor 30 (i.e., node 41). In general, the change in thevoltage drop across the active microbolometer causes a change in outputvoltage (Vout) 42. Therefore, as incident infrared radiation levelsincrease or decrease, this is reflected by the voltage level of outputvoltage (Vout) 42 increasing or decreasing, respectively.

[0068] In general, supply voltage 40 is used to adjust the load currentand thereby optimize the operating point of the circuit by settingoutput voltage 42 at a desired point within a range of output circuitryvoltage levels. Specifically, by setting the appropriate gate bias oftransistor 30 and appropriate voltage level of supply voltage 40, theoutput voltage (Vout) 42 is adjusted.

[0069] For example, supply voltage 40 may be a single voltage level setfor the entire array of microbolometers. Amplifier 32 and DAC 34 arethen used to supply a unique voltage bias to each correspondingthermally-shorted microbolometer 36 in the FPA to provide a fineadjustment or offset to the load voltage or the load current (Ibias).This corrects for the individual offset errors in the output signalsfrom each of the thermally-isolated microbolometers (e.g., the activemicrobolometers). By adjusting the offset for each microbolometercircuit, the nominal output voltage level of output voltage (Vout) 42for each circuit is adjusted to fall within a desired range.

[0070] To address the relative mismatch in temperature coefficient ofresistance (TCR) between the active microbolometer (in, circuit 330) andmicrobolometer 36 (the load microbolometer), resistors 26 and 38 areprovided. Resistor 26 is a variable resistor to generally provide fineadjustments to the composite TCR value of the active microbolometerportion of the circuit relative to the load microbolometer portion ofthe circuit. Thus, for the voltage divider network of resistors,resistor 26 adjusts the composite TCR of the active microbolometer andresistor 26 relative to microbolometer 36 and resistor 38. As anexample, circuit values for these circuit elements are 100 KΩ and 300 KΩfor the active microbolometer and microbolometer 36, respectively, butthese values are not limiting and may vary over a large range, such asfor example 50-200 KΩ and 150-600 KΩ, respectively. Exemplary circuitvalues for resistors 26 and 38 may, for example, vary within 0-10 KΩ and0-30 KΩ, respectively, but this range is not limiting and may vary overa wider range of values.

[0071] Resistors 26 and resistors 38 are typically resistors having adifferent TCR (generally lower) than their corresponding microbolometers(i.e., the active microbolometer and microbolometer 36). For example,resistor 26 may have a low TCR and the active microbolometer may have ahigher TCR relative to microbolometer 36. Consequently, by the properselection of resistance value for resistor 26, the combination ofresistor 26 and the active microbolometer provides a TCR that is muchcloser to the TCR of microbolometer 36 (or the TCR of the combination ofmicrobolometer 36 and resistor 38 if resistor 38 is present) than is theTCR of solely the active microbolometer. Therefore, the performance andbehavior of each microbolometer within the array is vastly improved overa range of substrate temperatures.

[0072] The following equation illustrates the combined or composite TCRfor a microbolometer in series with a variable resistor (i.e., theactive microbolometer and resistor 26) as a function of temperature.

TCR=(TCR _(Bo) R _(B)(T)/(R _(B)(T)+R _(Trim)))

[0073] TCR, TCR_(Bo), R_(B)(T), and R_(Trim) represent the effectivecombined TCR (labeled TCR), the TCR of the microbolometer (labeledTCR_(Bo)), the resistance of the microbolometer at a given temperature(labeled R_(B)(T)), and the resistance value of the variable resistor(e.g., to a first order constant as a function of temperature andlabeled R_(Trim)), respectively. This equation illustrates how thecombined TCR is adjusted depending upon the resistance value of thevariable resistor.

[0074] Resistor 38 provides the coarse adjustment for circuit 1000.Consequently by setting resistor 26, temperature compensation isprovided for the mismatch in relative TCR between the activemicrobolometer and the load microbolometer. A calibration procedure as afunction of the substrate temperature is performed to determine theappropriate value for resistors 26 and 38. Details of an exemplarycalibration procedure are provided herein.

[0075] The relative mismatch in TCR is driven by various factors, suchas pulse bias heating, non-uniformities among microbolometers, andrelative contact resistance between the active microbolometer and theload microbolometer and the substrate. Ideally, by accounting for therelative mismatch in TCR and offset as a function of substratetemperature, the output voltage for a given microbolometer circuit willbe well behaved. For example, for a certain level of received incidentinfrared radiation, the microbolometer circuit output voltage may fallwithin a small percentage (e.g., twenty percent) of the minimum andmaximum dynamic range over the desired substrate temperature range(e.g., from 250 to 350° C.).

[0076] It should be understood that FIG. 10a is an exemplary circuit toillustrate the relative TCR mismatch and temperature compensationtechniques and that numerous modifications and variations are possiblein accordance with the principles of the present invention. For example,resistor 38 may not be necessary, depending upon the characteristics ofthe microbolometers within the array. Resistors 26 and 38 may beimplemented as parallel resistance, rather than series, relative torespective microbolometers, or some combination of series and parallelresistance may be implemented. The circuit arrangement may also vary,such as by interchanging the positions of resistor 26 and resistor 38 orthe positions of circuit 330 and microbolometer 36. Furthermore, circuitpolarities may be inverted, such as for example by inverting powersupplies and substituting p-channel for n-channel transistors or viceversa as would be known by one skilled in the art. Additionally, one ormore techniques discussed or referenced herein may be combined orselectively implemented, depending upon the application or various otherfactors.

[0077] As an example of an alternative implementation, in accordancewith an embodiment of the present invention, FIG. 10c shows a circuit1070 illustrating a portion of a readout integrated circuit inaccordance with an embodiment of the present invention. Circuit 1070 issimilar to circuit 1050 of FIG. 10b, but resistor 26 is removed and acurrent source 272 is provided. The amount of current flowing throughthe active microbolometer (i.e., one of microbolometers 302(1) through302(N)) to produce a microbolometer bias current (labeled IbiasB) isreduced by the contribution of current by current source 272. Therefore,the voltage across the active microbolometer is reduced and the changein the contribution of current through the active microbolometer to themicrobolometer bias current (IbiasB) as a function of temperature isfractionally reduced. Thus, current source 272 has effectively loweredthe temperature coefficient of resistance (TCR) of the activemicrobolometer.

[0078] Current source 272 may be employed to provide temperaturecompensation within the readout integrated circuit. Current source 272,for example, may be a fixed or a variable current source and may bevaried or set in a similar fashion as discussed herein for resistor 26(e.g., as discussed in reference to FIGS. 12-17) to provide temperaturecompensation.

[0079] In general as an example, circuit 1000 in FIG. 10a (as well as,for example, other circuits illustrated herein) can be implemented in anarray configuration, with a portion of circuit 1000 placed in the unitcell while the remainder is placed outside of the unit cell, such as inthe column amplifier. For example, circuit 330 may be solely placedwithin the unit cell array (along with associated selection circuitry,if desired, such as switches 304).

[0080]FIG. 11 shows a circuit 1100 illustrating a portion of a readoutintegrated circuit 1102 and circuit 330 (or a portion of amicrobolometer array) in accordance with an embodiment of the presentinvention. Circuit 1102 provides temperature compensation for circuit330 in accordance with an embodiment of the present invention.

[0081] Circuit 1100 is similar to circuit 1000 of FIG. 10a, but includesa reference path 62. Reference path 62 includes thermally shortedmicrobolometers 66 and 74, variable resistor 68, a transistor 70, anamplifier 72, and a DAC 64.

[0082] DAC 64 provides a reference voltage to amplifier 72, which isused to appropriately bias transistor 70. DAC 64 and resistor 68 areadjusted to provide a reference voltage for amplifier 28. Amplifiers 32and 72 may have their reference voltage provided by a DAC or thereference voltage may be provided to amplifier 32 and/or 72 by a setreference voltage level (e.g., ground). Furthermore, microbolometer 66and/or microbolometer 74 may be replaced by a resistor, which wouldprovide the necessary temperature dependent reference behavior.

[0083] Reference path 62 will be affected by changes in substratetemperature in a similar fashion as the remaining portions of circuit1102. Consequently, the reference voltage to amplifier 28 will vary intemperature and, therefore, reference path 62 provides additionaltemperature compensation. Additionally, power supply noise from supplyvoltage 40 and the reference voltage (VDETCOM) are reduced by the commonmode input to amplifier 28.

[0084]FIG. 12 shows a top-level flowchart 100 of a calibration processin accordance with an. embodiment of the present invention. Flowchart100 includes steps 102 through 110 for calibrating a microbolometer FPA.Step 104 is a required step and steps 102 and 106 through 110 may beoptional steps, depending upon the microbolometer FPA behavior orperformance, the desired application, and required performance. FIGS. 13through 16 provide exemplary detailed flowcharts pertaining to steps 102through 110.

[0085] The external resistance is calibrated in step 102. The term“external resistance” refers, for example, to the resistance of aresistor such as resistor 38 of FIG. 10a, which is typically placedoutside of the unit cell and is not part of the variable (or trim)resistance (e.g., resistor 26 of FIG. 10a). The external resistance orthe value of the external resistor may be digitally selectable and/ormay be a global resistor and may be on or off-chip (i.e., on or off theFPA or the ROIC). Therefore, one external variable resistor or a fewexternal variable resistors may be sufficient for a large microbolometerFPA. For example, as each microbolometer in the array is sampled, theglobal external resistor is set to its calibrated value, determinedduring the calibration process, corresponding to that particularmicrobolometer, column, group, or array of microbolometers. As discussedabove, depending upon the behavior of the microbolometers in the FPA, anexternal resistor may not be required.

[0086] The variable resistance and offset is calibrated for eachmicrobolometer in step 104. The variable resistance or trim resistancerefers, for example, to the resistance of a resistor (a trim resistor)such as resistor 26 in FIG. 10a. For example, step 104 determines theamount of resistance to be placed in series with each activemicrobolometer in the FPA. Step 104 also determines the amount of offsetto be applied for each microbolometer in the FPA. As an example, thedetermined offset for each microbolometer may be set by using DAC 34 tocontrol the gate bias of transistor 30 via amplifier 32 in FIG. 10a .

[0087] Step 106 provides fine offset correction calibration for eachmicrobolometer circuit output over the desired substrate temperaturerange. Various techniques may be employed to provide a fine correctionto each microbolometer circuit output after step 104 and possibly step102 are performed, because these steps then provide a correctablemicrobolometer circuit output over a wide range of substratetemperature. The techniques may include various mathematical best-fit oroffset correction algorithms or look-up table methods to determine thefine offset correction factor for a given temperature. For example,Lagrange terms enable a polynomial offset correction to be generated inreal-time for each microbolometer that compensates for variations inmicrobolometer circuit output over FPA substrate temperature.

[0088] Step 108 provides gain calibration for each microbolometer. Thegain terms normalize the response of each microbolometer to incidentinfrared radiation. This step may simply determine the gain termindependent of FPA substrate temperature or, in a more general fashion,determine the gain term as a function of FPA substrate temperature.Similar mathematical best-fit, correction algorithms, or look-up tablemethods can be provided for these terms. Step 110 provides an additionalfine offset, if required, for each microbolometer. The offset also maybe a function of FPA substrate temperature.

[0089]FIG. 13 is a detailed flowchart 120 for step 102 of flowchart 100in FIG. 12. Flowchart 120 provides exemplary calibrations steps forcalibrating the external resistor. Step 122 sets the trim resistor foreach microbolometer to a target value, such as the median value of thetrim resistor range. The FPA temperature is then set to a value (i.e.,T1) within the desired calibration or operation temperature range (step124). For example, T1 may represent the value of the minimum operatingtemperature range. The external resistor is then set to one of its “n”possible values (step 126) and the offset is calibrated for eachmicrobolometer (step 128), where the offset may be calibrated using theprocedure described below. The offset value and microbolometer circuitoutput value, obtained after application of the offset value, is stored(step 130) and steps 126 through step 128 are repeated for each of the npossible external resistor values (step 132). The result is n pairs ofexternal resistor and offset values along with each correspondingmicrobolometer circuit output value.

[0090] The FPA temperature is then changed to another value (e.g., T2)within the desired calibration range (step 134). The stored externalresistor and offset values are applied, for each value of n, and themicrobolometer circuit output value is recorded (step 136). For eachvalue of n, step 138 calculates the difference between themicrobolometer circuit output from step 136 (i.e., at T1) and themicrobolometer circuit output from step 132 (i.e., at T2) and thencalculates the average difference across the full array ofmicrobolometers. Step 140 selects the external resistor valuecorresponding to the smallest average difference obtained from step 138,with this resistor value being the calibrated value of the externalresistor for the entire microbolometer FPA.

[0091]FIG. 14 is a detailed flowchart 150 for the trim resistancecalibration in step 104 of flowchart 100 in FIG. 12. Flowchart 150provides exemplary calibration steps for calibrating the trim resistor.Step 152 sets the FPA substrate temperature to one extreme of thedesired operating or calibration temperature. range (e.g., T1). The trimresistor is set to one of “m” possible values (step 154), such as theminimum value, and then the offset is calibrated (step 156) using aprocedure, such as the one described below. The offset value and theresulting microbolometer circuit output value, after application of theoffset value, are recorded for the given trim resistor value (step 158).Step 160 repeats steps 154 through 158 for each of the m possible trimresistor values, which results in m pairs of trim resistor/offset valuesand corresponding microbolometer circuit output values.

[0092] The FPA substrate temperature is then changed to a value (T2) atthe opposite extreme as the prior value (T1) of the desired calibrationor operating temperature range (step 162). For each value of m, thecorresponding trim resistor value and offset value obtained in steps 154through 160 are applied and the microbolometer circuit output value isrecorded (step 164). For each value of m (FIG. 14—step 166), thedifference is calculated between the microbolometer circuit output fromstep 164 (i.e., at temperature T2) and the microbolometer circuit outputobtained from step 158 (i.e., at temperature T1). Step 168 selects thetrim resistor value and associated offset value that corresponds to theminimum difference from the results of step 166. These values are thecalibrated values for the trim resistor and offset. Note that, ifdesired, the offset can be re-calibrated at a different FPA temperaturevalue or with a different target value. This would provide a widertemperature operating range and more well-behaved performance.

[0093] For step 104 of flowchart 100 in FIG. 12, the offset value isdetermined for each microbolometer in the FPA. The offset value, forexample, can be determined for each microbolometer by using a binarysearch to find the offset value that adjusts the microbolometer circuitoutput value closest to a desired value (i.e., microbolometer circuitoutput target value). The temperature of the FPA substrate and otherparameters, such as the flux incident on the FPA, should generally notvary substantially while the offset calibration is in process.

[0094]FIG. 15 is a detailed flowchart 180 for step 106 of flowchart 100in FIG. 12. Flowchart 180 provides exemplary calibrations steps forcalibrating the fine offset correction (e.g., Lagrange) terms for amicrobolometer in the FPA array. However, the exemplary procedure couldbe employed in the more general case to calibrate many pixelssimultaneously. Step 182 sets the FPA temperature to a value within thedesired calibration or operating range and records the measuredtemperature value (having temperature units, such as Kelvin or Celsius,or units of volts that correspond to a given temperature). For thistemperature, the microbolometer circuit output is recorded after theapplication of the calibrated trim resistor and offset values (step184).

[0095] The FPA temperature is then changed, at step 186, to anothervalue within the desired temperature range and steps 182 and 184 arerepeated. Step 188 repeats step 186 a minimum of K+1 times, where Krepresents the desired order of the polynomial correction. For example,a minimum of four terms is stored if the third order polynomialcorrection is desired. The polynomial correction results generallyimprove if two of the K+1points are at the opposite extremes of thedesired calibration range.

[0096] The gain of each microbolometer can be calibrated using atwo-point calibration process (e.g., at two different values of incidentflux) at any arbitrary FPA temperature. Alternatively, the gain of eachmicrobolometer can be calibrated as a function of FPA temperature, suchas in the calibration process described below. Both procedures aresimilar to the fine offset (e.g., Lagrange) correction described abovein reference to FIG. 15, but the two procedures (i.e., gain and fineoffset) differ from each other in that instead of storing eachmicrobolometer circuit output at a single value of incident flux, eachmicrobolometer circuit output is stored for two values of incident flux.

[0097]FIG. 16 is a detailed flowchart 200 for step 108 of flowchart 100in FIG. 12. Flowchart 200 provides exemplary calibration steps forcalibrating the gain of each microbolometer. Step 202 sets the FPAtemperature to a value within the desired calibration or operating rangeand the temperature value is recorded (in units of temperature, such asKelvin or Celsius, or in units of voltage that correspond to a giventemperature). Step 204 records the microbolometer circuit outputdifference for two flux levels or responsivity for that temperature foreach microbolometer. Step 206 changes the FPA temperature to anothervalue within the calibration or operating range and the temperaturevalue and each microbolometer circuit output is recorded. Step 206 isrepeated (in step 208) a minimum of K+1 times, where k represents thedesired order of the polynomial fit of the gain terms.

[0098]FIG. 17 illustrates a compensation process 220 in accordance withan embodiment of the present invention. Compensation process 220illustrates generally the overall compensation process for providing anoptimal output from each microbolometer in the FPA over the desired FPAtemperature range. The microbolometer FPA is represented symbolically byan FPA 222. As shown, each microbolometer in the array receives a trimresistor (Rtrim_(i), where i ranges from 1≦i ≦maximum number ofmicrobolometers in the array) and an offset calibration (Offset_(i))adjustment. The trim resistor calibration and the offset calibrationadjust each microbolometer circuit output over the calibratedtemperature range. An external resistor (Rext) calibration is alsooptionally performed as described above, depending upon microbolometerFPA behavior. There may be an external resistor digitally selectable foreach microbolometer or there may be one or more global externalresistors that are calibrated for the entire microbolometer FPA or somecorresponding portion of the microbolometer FPA.

[0099] The microbolometer circuit outputs from FPA 222 are combined inblock 224 with the calibrated temperature-dependent fine (e.g.,Lagrange) offset 230. The fine offset may be determined in any of anumber of methods or techniques, as discussed herein. FIG. 17 refers tothe fine offset as Lagrange offset 230, which is one exemplary method,but the fine offset is not intended to be limited solely to thisexemplary method. Lagrange offset 230 provides the calibrated polynomialcorrection values for each microbolometer circuit output, which can besummed with each microbolometer circuit output from FPA 222.

[0100] The application of Lagrange offset 230 refines the microbolometercircuit output behavior and provides more uniform data at the dataprocessor (i.e., reduces the curve or bow in microbolometer circuitoutput over temperature). Lagrange offset 230 receives as inputs themeasured substrate temperature and the Lagrange terms (LagrangeTerm_(i)), which are used to generate the Lagrange offset terms uniquelyfor each microbolometer in the array.

[0101] A block 226 receives the microbolometer circuit outputs, afterapplication of the Lagrange offsets, and multiplies the microbolometercircuit outputs by a corresponding calibrated temperature dependent gain232. The gain adjusts each microbolometer circuit output to provide amore uniform response to incident flux. As shown, the gain istemperature dependent and receives as inputs the measured substratetemperature and the gain terms (Gain Term_(i)), which are used togenerate the temperature dependent gain uniquely for each microbolometerin the array.

[0102] A block 228 receives the microbolometer circuit outputs, afterapplication of the gain adjustment, and sums the microbolometer circuitoutputs with additional offset terms (Offset_(i)), with the offset forblock 228 typically differing from the offset input to FPA 222. Forexample, the offset term is updated periodically during camera operationusing a shutter, a chopper, or a scene-based algorithm.

[0103] It should be appreciated that the implementation of the trimresistor (or current source 272) within each microbolometer circuitprovides the correctable microbolometer FPA performance over a widetemperature range. The correctable microbolometer FPA performance overthe calibrated temperature range then permits the application ofLagrange offset, gain, and offset calibration over the wide calibratedtemperature range. It should also be appreciated that the principles ofthis invention may be implemented or applied to a wide variety ofcircuit devices and materials. Accordingly, the embodiments describedherein are only exemplary of the principles of the invention and are notintended to limit the invention to the specific embodiments disclosed.

[0104] Embodiments described above illustrate but do not limit theinvention. It should also be understood that numerous modifications andvariations are possible in accordance with the principles of the presentinvention. Accordingly, the scope of the invention is defined only bythe following claims.

We claim:
 1. A circuit comprising: a plurality of microbolometersforming a microbolometer array, wherein contacts within themicrobolometer array are shared among the microbolometers; means forselecting from among the microbolometers in the microbolometer array andproviding a corresponding output signal; and means for providingtemperature compensation for the output signal.
 2. The circuit of claim1, wherein the contacts are shared between adjacent ones of themicrobolometers in a column and the contacts are shared between themicrobolometers in different columns in the microbolometer array.
 3. Thecircuit of claim 1, wherein the plurality of switches comprise a firstset of switches adapted to apply a reference voltage to correspondingones of the plurality of microbolometers and a second set of switchesadapted to route the output signal from corresponding ones of theplurality of microbolometers.
 4. The circuit of claim 3, wherein thefirst set of switches are initially asserted and the second set ofswitches initially deasserted, with the first set of switchessequentially deasserted as corresponding ones of the second set ofswitches coupled to the same contacts are sequentially asserted untilall of the second set of switches are asserted.
 5. The circuit of claim3, wherein one of the first set of switches is asserted for every two ofthe second set of switches to provide the output signal for two of themicrobolometers in corresponding columns.
 6. The circuit of claim 1,wherein the means for providing temperature compensation comprises atleast one resistor associated with the plurality of microbolometers, theat least one resistor adapted to be calibrated to provide temperaturecoefficient of resistance compensation for the microbolometers.
 7. Thecircuit of claim 6, wherein the means for providing temperaturecompensation further comprises at least one bias circuit adapted toprovide a bias for the plurality of microbolometers.
 8. The circuit ofclaim 7, wherein the bias circuit comprises a load microbolometer. 9.The circuit of claim 8, wherein the bias circuit further comprises aresistor adapted to provide temperature coefficient of resistancecompensation for the load microbolometer.
 10. The circuit of claim 6,wherein the means for providing temperature compensation furthercomprises at least one reference path associated with at least one ofthe plurality of microbolometers, the reference path adapted to providea reference voltage.
 11. The circuit of claim 1, further comprising adata processor adapted to provide uniformity-correction data for theplurality of microbolometers and to control non-uniformity correctionsof the output signals.
 12. The circuit of claim 11, wherein theuniformity-correction data comprises trim resistance values and offsetvalues for the plurality of microbolometers.
 13. The circuit of claim12, wherein the uniformity-correction data further comprises fine offsetvalues and gain calibration values.
 14. The circuit of claim 12, whereinthe uniformity-correction data further comprises at least one externalresistor value and additional fine offset values.
 15. The circuit ofclaim 1, wherein the means for providing temperature compensationcomprises at least one current source associated with the plurality ofmicrobolometers.
 16. The circuit of claim 15, wherein the means forproviding temperature compensation further comprises at least one biascircuit adapted to provide a bias for the plurality of microbolometers.17. The circuit of claim 16, further comprising a data processor adaptedto provide uniformity-correction data for the plurality ofmicrobolometers and to control non-uniformity corrections of the outputsignals.
 18. The circuit of claim 17, wherein the uniformity-correctiondata comprises a current value for the current source and offset valuesfor the plurality of microbolometers.
 19. A method of providingcalibrated output signals from a microbolometer focal plane array havingshared contacts, the method comprising: selecting at least one row ofthe microbolometer focal plane array to provide corresponding outputsignals from microbolometers in the row; providing a trim resistor valueto provide temperature compensation for at least one microbolometer inthe row; and providing an offset value to provide temperaturecompensation for at least one microbolometer in the row.
 20. The methodof claim 19, wherein the shared contacts are shared between adjacentmicrobolometers in columns of the microbolometer focal plane array. 21.The method of claim 19, wherein the shared contacts are shared betweenadjacent microbolometers in columns of the microbolometer focal planearray and between microbolometers in different columns of themicrobolometer focal plane array.
 22. The method of claim 19, whereinthe selecting comprises: applying a reference voltage to themicrobolometers in the row; and providing a signal path from themicrobolometers in the row.
 23. The method of claim 19, wherein theselecting comprises: applying a reference voltage to the microbolometersin the microbolometer focal plane array; and selecting sequentially eachrow of the microbolometer focal plane array to provide a signal pathfrom the microbolometers in the row, wherein the reference voltage isremoved from the previous row prior to selecting the next row throughthe shared contact.
 24. The method of claim 19, further comprisingcalibrating the microbolometer focal plane array to determine the trim.resistor values and the offset values over a desired temperature range.25. The method of claim 19, further comprising providing a fine offsetand a gain calibration to the output signals.
 26. The method of claim25, further comprising providing an additional offset to the outputsignals.
 27. A microbolometer focal plane array comprising: a pluralityof microbolometers forming a microbolometer array, wherein contactswithin the microbolometer array are shared by the microbolometers; afirst plurality of switches adapted to provide a reference signal torespective ones of the plurality of microbolometers; and a secondplurality of switches adapted to receive an output signal fromrespective ones of the plurality of microbolometers, wherein the firstand second plurality of switches are initially asserted and deasserted,respectively, with one of the switches from the first pluralitydeasserted prior to one of the switches from the second plurality beingasserted which couple to the same contact, with this switching patternrepeated for the first and second plurality of switches until the secondplurality of switches are all asserted.
 28. The microbolometer focalplane array of claim 27, wherein the contacts being shared are locatedbetween the microbolometers in a column.
 29. The microbolometer focalplane array of claim 27, further comprising: a resistor adapted toprovide temperature compensation for at least one of themicrobolometers; and a bias circuit, coupled to the resistor, adapted toprovide an offset for at least one of the microbolometers.
 30. Themicrobolometer focal plane array of claim 29, further comprising areference path for at least one of the microbolometers, the referencepath adapted to provide a temperature compensated reference voltage. 31.The microbolometer focal plane array of claim 29, wherein themicrobolometer focal plane array is couplable to a processor adapted toprovide uniformity-correction data for the microbolometer focal planearray.
 32. The microbolometer focal plane array of claim 31, wherein theuniformity-correction data comprises a resistance value for the resistorand an offset value for the offset.
 33. The microbolometer focal planearray of claim 31, wherein the processor controls non-uniformitycorrections to the output signals.
 34. The microbolometer focal planearray of claim 33, wherein the non-uniformity corrections comprise atleast one of a fine offset, a gain calibration, and an additionaloffset.
 35. The microbolometer focal plane array of claim 29, whereinthe resistor and the bias circuit are adapted to be calibrated toprovide temperature compensation for the microbolometers.
 36. Themicrobolometer focal plane array of claim 27, further comprising: acurrent source adapted to provide temperature compensation for at leastone of the microbolometers; and a bias circuit, coupled to the currentsource, adapted to provide an offset for at least one of themicrobolometers.
 37. The microbolometer focal plane array of claim 36,wherein the microbolometer focal plane array is couplable to a processoradapted to provide uniformity-correction data for the microbolometerfocal plane array.